We propose developing a trans-molecular RNA-switch for scientists to measure miRNA activity in-vivo. While there are numerous methods to quantify miRNAs in vitro, we are not aware of any method that allows for in vivo analysis. The ability to observe specific miRNA generation in living single cells without requiring the destruction of the cell would be a significant tool. We are pioneering an RNA-based switch technology called structurally interacting RNAs (sxRNA) which utilizes post-transcriptional gene regulation as a reporter for miRNA detection. Normally, RNA-binding proteins (RBP) associate with a 3'stem-loop structure to facilitate translation of an upstream coding region by as much as an order of magnitude. It is possible to modify the mRNA to modulate translation of the reporter gene by controlling the binding of RBP. This is accomplished by altering the natural stem-loop structure so that it does not form unless an additional RNA, such as a miRNA, binds and stabilizes the functional structure by base- pairing with the flanking regions of the custom designed stem-loop. Our goal with this proposal is first to evaluate the switch mechanism in-vitro and measure the specificity of interaction and signal strength possible. Secondly, we will measure the effect on translation and determine whether this switching mechanism is effective in a cell. Success at the product level using sxRNA as a diagnostic tool should ideally position the technology for additional uses. It could be effective anywhere that miRNA expression levels are an indicator of disease, cell or tissue type, or condition. sxRNA could be an RNA-based alternative to gene therapy for protein deficiency diseases, such as cystic fibrosis, or a cancer therapy. PUBLIC HEALTH RELEVANCE: While there are numerous methods to quantify miRNAs in vitro, we are not aware of any method that allows for in vivo analysis. The ability to observe specific miRNA generation in living single cells without requiring the destruction of the cell would be a significant tool. For example, stem cell researchers could ensure stem cells had not differentiated by in-vivo detection of miRNAs that are preferentially expressed during differentiation.